The present invention relates to a process for determining the unbalance of a driven rotating rigid rotor with respect to at least one compensation plane of the rigid rotor according to relative position and size.
A rotor to be balanced is considered to be a rigid rotor as long as it is driven below its first critical speed and whereby the effects of the unbalance are determined by means of oscillation transducers on the support stands of a balancing machine in which the rigid rotor to be examined is mounted.
In this context, two different possibilities for balancing are distinguished. First subcritical balancing where the characteristic frequency of the system "rotor in its balancing supports" is higher than the speed at which the rigid rotor to be examined is being driven. Secondly, there is a type of supercritical or soft balancing machine where the critical speed of the system "rotor in its balancing supports" is smaller than the speed at which the rigid rotor is being driven.
Regardless of subcritical or supercritical support of the rigid rotor to be examined, until now, the measurement of the effect of the unbalance has been carried out at a constant speed of the rigid rotor to be examined, whereby, in order to obtain as accurate a measurement as possible of the relative position and of the size of the unbalance effect in the two support stands, it is necessary to carry out several measurement rotations. As a result of the necessary acceleration time, the measuring time and the braking time, there is a lower limit for the balancing time for the duration of a measuring operation, below which the operation cannot fall due to physical reasons.
It is also a known procedure, by using a so-called coasting machine, to support the rigid rotor to be examined in a balancing machined to use the driving motor in order to accelerate the rotor to a speed of the rigid rotor to be examined which is higher than the measuring speed. Subsequently, the rigid rotor is disengaged from the motor and, while it is coasting, the unbalance oscillations are determined in the support stands on the basis of relative position and size. Such methods are even more time-consuming when the rigid rotor to be examined is not additionally braked after having gone beyond the measuring speed.
From the VDI Progress Reports, Series 11, No. 143, Dusseldorf, VDI Publishers 1991 "Balancing Flexible Rotors After Only One Transient Measuring Operation" by M. S. Rama de Silva, it has become known to balance flexible rotors after only one transient measuring operation in such a manner that, during the passage of the flexible rotor through its different critical speeds, by picking up the wave shape of the rotor at various places on the rotor, measured values are obtained on the basis of which a subsequent balancing of the rotor is possible. The rotor no longer displays any excursions when passing through the critical speeds once again. In order to balance this rotor in the subcritical range as well, that is, in order to eliminate the effects of the unbalance on the supports, with such a rotor it is necessary to carry out one more measuring operation in the subcritical range. Such a procedures however, is extremely time-consuming, since the rotor in this speed range must be seen as a rigid element whose support forces have not yet been eliminated. For this purpose, it would have to be once again accelerated to a measuring speed below the first critical speed, and several measurements would have to be made at this measuring speed. Then the element would have to be braked once again.
Moreover, one should also note that the measuring speeds of rigid rotors are subject to a certain fluctuation so that, in spite of a larger number of measurements during the measuring operation, the quality of the unbalance measurement is additionally influenced.